The subject matter disclosed herein generally relates to load estimation and, more particularly, to load estimation for a twin engine helicopter.
Gas turbine engines typically include a compressor section, a combustor, and a turbine section, arranged in flow series with an upstream inlet and a downstream exhaust. Initially, air flows through the compressor section where it is compressed or pressurized. The combustor then mixes and ignites the compressed air with fuel, generating hot combustion gases. These hot combustion gases are then directed from the combustor to the turbine section where power is extracted from the hot gases by causing blades of the turbine to rotate.
Gas turbine engines may include one or more spools. For example, small-scale engines may generally use a one-spool design with co-rotating compressor and turbine sections, while larger-scale engines may generally comprise a number of coaxially nested spools. The multiple spools may operate at different pressures, temperatures, spool speeds, and directions. For instance, two-spool designs may include a high pressure spool (or high spool) and a low pressure spool (or low spool). The high pressure spool may include a high pressure turbine driving a high pressure compressor, and the low pressure spool may include a low pressure turbine driving a low pressure compressor.
Turboshaft engines, a type of gas turbine engine typically used on helicopters, rotorcrafts, and power plants etc., generally include a free power turbine spool for extracting heat energy from turbine exhaust and converting it into output shaft power. The free power turbine spool may comprise a power turbine that drives an external load that is an integrated system of a main rotor, a tail rotor, a drive train, and a gear box of the helicopter. Helicopter flight maneuvers, which involve a change in collective pitch, rapidly change the load or power demand on the power turbine in various flight conditions. In particular, aggressive helicopter flight maneuver generally poses a massive design challenge to engine fuel control for rejecting rotor load disturbance in hostile environment. In order to achieve ideal handling qualities for the airframe, it is important to maintain a constant rotor speed or minimize rotor excursion (i.e. deviation from the constant rotor speed) while promptly delivering the requested change in power demand on the power turbine.
Further, rotor torsional resonance phenomena can impose a significant design challenge to engine power delivery for helicopter flight control system. The rotor resonance is caused by the coupling of natural modes of the drive train interacting with the main rotor and the tail rotor. The torque and speed measurements of power turbine are typically disturbed by rotor resonance of main rotor and tail rotor. In order to mitigate the impact of rotor torsional resonance, current control design sometimes uses a damping approach with performance compromise. Alternatively, another method includes taking advantages of all available sensor measurements of engine and aircraft for accurately estimating the engine output shaft power disturbed by rotor resonance so as to improve flight control quality at various power levels.
Accordingly, there exists a need for an engine control system that can not only accurately estimate engine output shaft power but also promptly match the change in power demand while maintaining a constant rotor speed and abating the impact of rotor resonance.